A mask drawing apparatus is an apparatus to draw a desired pattern by irradiating an electron beam to a mask substrate (blank) comprising a substrate (mainly glass substrate) and a light shielding film (for example, chromium (Cr)) formed on the substrate. A resist film is formed on a surface of the mask substrate, and to draw the desired pattern, the resist film is exposed to the electron beam.
The mask substrate is grounded at the time of the drawing by the electron beam. This is because without the mask substrate being grounded, electric charges accumulate on the mask substrate due to the electron beam to bend a trajectory of the electron beam or to cause a blur due to the diffusion of the electron beam. It is impossible to draw a desired pattern on the mask substrate when the bending of the trajectory of the electron beam or the blur of the electron beam is occurred.
Because of this, in the mask drawing apparatus, at the time of the drawing by the electron beam, a grounding body is set on the mask substrate. Because the electric charges accumulating on the mask substrate due to the electron beam are discharged via the grounding body, the charging of the mask substrate can be prevented.
However, it is known that an unexpected increase of a contact resistance value between the grounding body and the mask substrate (hereinafter, referred to as a resistance value) sometimes occurs. Further, when the grounding body is set on the mask substrate, the resistance value sometimes differs depending on the direction in which the grounding body is set. There are various possible factors that cause such phenomenon, and a possible factor is, for example, that the grounding body does not reach a light shielding film of the mask substrate. If the drawing by the electron beam is performed in such a case, the electric charges accumulate on the mask substrate to bend the trajectory of the electron beam or to blur the electron beam. As a result, it is impossible to draw a desired pattern on the mask substrate. Therefore, there have conventionally been proposed various methods that can reduce the resistance value between the grounding body and the mask substrate.